The components of high-temperature mechanical systems, such as, for example, gas-turbine engines, must operate in severe environments. For example, hot section components of gas turbine engines, e.g., turbine blades and/or vanes, exposed to hot gases in commercial aeronautical engines may experience surface temperatures of greater than 1,000° C. Economic and environmental concerns, i.e., the desire for improved efficiency and reduced emissions, continue to drive the development of advanced gas turbine engines with higher gas inlet temperatures. As the turbine inlet temperature continues to increase, there is a demand for components capable of operating at such high temperatures.
Components of high-temperature mechanical systems may include ceramic and/or superalloy substrates. Coatings for such substrates continue to be developed to increase the operating capabilities of such components and may include thermal barrier coatings (TBC) and environmental barrier coatings (EBC). In some examples, thermal barrier coatings (TBC) may be applied to substrates to increase the temperature capability of a component, e.g., by insulating a substrate from a hot external environment. Further, environmental barrier coatings (EBC) may be applied to ceramic substrates, e.g., silicon-based ceramics, to provide environmental protection to the substrate. For example, an EBC may be applied to a silicon-based ceramic substrate to protect against the recession of the ceramic substrate resulting from operation in the presence of water vapor in a high temperature combustion environment. In some cases, an EBC may also function as a TBC, although a TBC may also be added to a substrate in addition to an EBC to further increase the temperature capability of a component.